Glutamate is the most abundant stimulatory neurotransmitter within the brain and glutamate receptors are thought to play a major role in physiological processes such as learning and memory. To compliment and extend data from previous immunocytochemical studies, mRNA distribution patterns for the following glutamate receptor subunits were examined in the temporal cortex of rhesus macaques NMDAR1, GluR1, GluR2, and GluR3. Using 35S-labeled cRNA antisense probes, sections of temporal cortex at the level of the caudal hippocampus and lateral geniculate body were hybridized overnight at 60 C. Following various washes, RNase treatment, and a criterion wash at 70 C in 0.1X SSC, the sections were apposed to Hyperfilm for autoradiography. The in situ hybridization patterns for the NMDA and AMPA receptor subtypes (i.e., NMDAR1 and GluR1, GluR2, GluR3, respectively) were similar in both distribution and intensity. High levels of hybridization were seen in the dentate gyrus and the CA3, followed by slightly lower levels in the CA1, dentate hilus, entorhinal and surrounding temporal cortex. Despite high levels of NMDAR1 mRNA in the lateral geniculate body there was an apparent lack of GluR1, GluR2, and GluR3 mRNA in this region. Also of note was the differential expression of GluR1 mRNA in the temporal cortex. Unlike the other glutamate receptor subunits examined, GluR1 mRNA expression was lacking in an intermediate layer of the cortex, but still present in apical and basal layers. The apparent colocalization of different glutamate receptor subunits in many areas is of integrative importance because the physiological properties of glutamate receptors is determined by their subunit composition. On the other hand, the lack of specific receptor subunits may be equally important for regional function. (Findings from this study were presented in 1995 at the Annual 640022g of the Society for Neuroscience, held in San Diego, CA).